VoLTE will come to devices that are capable of it with likely a combination of an iOS update and a carrier settings update... as to what devices will be compatible, it remains to be seen... I recall seeing the iPhone5 and above would be compatible when carriers enable it on their networks and they release the firmware updates.

He was also saying it only works if the other person is also on a supported device.

Sent from my Gold iPad Air using Tapatalk

True. And if you drop from LTE to 3G, your call will drop. The iPhones also don't support the video calling feature, and the cross platform video calling without needing to settle on a specific service was probably the best feature of Advanced Calling 1.0